1. Field of the Invention
The present invention relates to a powder beam etching method for injecting fine particles from a nozzle against a surface of a workpiece (hereinafter referred to as the work) for etching it.
2. Description of the Related Art
A nozzle used in conventional powder beam etching has a rectangular type nozzle 51 having a rectangular opening portion such as shown in FIG. 5. In the case where powder 52 is injected from the rectangular nozzle 51 against a surface 53 of a work 51, a non-uniform distribution of the etching depth tends to occur in the manner shown in FIG. 5. A range or width A wherein the etching depth remains relatively uniform depends upon the type of nozzle 51 but is normally 0.5 to 5 mm. Further, the amount of the powder 52 which is injected from the nozzle 51 per unit injection time varies as shown in FIG. 6. For example, in the case wherein the target injection amount is 10 g/min, the amount has been found to vary in the range of about 10 g.+-.2 g. Namely, there tends to be a variation of .+-.20%.
In order to suppress the above-described variation in etching depth, in the conventional technique, as shown in FIG. 7, after the nozzle 51 have been repeatedly scanned and pitch-fed to etch the entire surface 53 of the work, the nozzle is moved back to the scanning starting point along exactly the same path. As a result, it is possible to improve the uniformity of the etching depth up to .+-.14%.
However, in case of the fine etching, in many cases, a uniformity in etching depth within .+-.10% is required. This requirement cannot be met by the conventional etching. As a result, the application of the powder beam etching is unduly limited.
In view of this defect, an object of the present invention is to provide a powder beam etching method which is capable of enhancing uniformity in etching depth.